The steem token is designed to lose value over time (due to inflation of the number of tokens - similar to how more Bitcoins are created every ten minutes or so). To overcome the value loss from holding steem you can "power up" and thus become more of a long term stakehoder in the system (your value is locked up for 2 years, you can only withdraw about 1% a week), or you can convert your steem to Steem Dollars which accrue interest and are loosely pegged to the US$ such that you can always convert them to about a dollars worth of steem in the future.